The different needs and requirements of wheelchair users have resulted in a variety of styles and types of wheelchairs. Most existing designs of wheelchairs can be viewed as derivations from the traditional institutional wheelchair, which can be characterized by rugged construction designed to provide maximum stability to the user. Based on this primary design consideration, extensive use of heavy gauge metal, such as steel or aluminum, for members or components is common in wheelchair designs, resulting in very stable and sturdy wheelchairs, but at the expense of weight and easy portability.
There are lightweight wheelchairs for racing, basketball and other sports events. Although designed for lightness, impact resistance and maneuverability, they are not comfortable to use for more than very limited periods because the design for maximizing power or energy of the user adversely affects the sitting position of the user.
Some wheelchairs are foldable so that they can be stowed when not in use. It is important to have the foldable wheelchair as compact as possible when in a folded state. In many wheelchairs, the folded state is quite large because the wheels and wheel hubs extend outwardly, adding to the width of the wheelchair, even in its folded state. Further, if the wheels remain on the wheelchair in its folded state, the wheels themselves add to the difficulty in positioning the wheelchair in a compact space, such as the trunk or rear seat portion of a car. Examples of such foldable wheelchairs are found in U.S. Pat. Nos. 4,101,143 and 4,273,350 which describe designs foldable inwardly toward the medial plane of the wheelchair. Despite such folding capability to reduce the width of the wheelchairs, the overall heights of the wheelchairs remain the same, making the wheelchair bulky and difficult to handle.
There are some foldable wheelchairs having detachable wheels. For example, U.S. Pat. No. 4,650,201 describes a lightweight wheelchair having detachable wheels and a back support for the seat which is forwardly foldable. However, this design employs numerous linkages and strut supporting members which are not foldable. Thus, in its folded state, the wheelchair structure remains bulky and awkward to handle.
There has also been at least one foldable lightweight wheelchair advertised to the market. That chair was designed with the caster essentially under the chair seat and the caster supports mounted such that the chair was a "center of gravity" chair. Such chairs are known to be quite unstable and have a definite tendency for the user to tip backward and overturn the chair. Such chairs require special operating techniques for the user, and the user must become trained to maneuver the chair without tipping it over. Many persons have physical conditions which do not permit them to use such a chair, whether or not the chair is foldable.
There is consequently a need for an improved wheelchair which combines stability and maneuverability, as found in "sports" models, with exceptional lightness and comfort. There is also a need for a wheelchair in which strength and resilience are present with minimum structure, as well as a need for a wheelchair which is both conveniently portable and adaptable to easy storage.